The present disclosure relates to a switching element driving circuit that amplifies a switching control signal and drives a switching element.
To drive a switching element of an inverter that converts electrical power between direct current and alternating current, a drive circuit that amplifies electrical power of a switching control signal generated by a control circuit may be provided. As such a drive circuit, a push-pull circuit such as that described in JP 2004-242475 A may be used (see reference sign 10a of FIG. 1, [0030], etc.). Meanwhile, when the inverter drives a high-output electrical apparatus, a direct-current side voltage may be a high voltage on the order of 200 to 400 [V]. Such high-voltage direct-current electrical power is supplied from a so-called high-voltage direct-current power supply. On the other hand, the control circuit that generates a switching control signal generally has an operating voltage of 5 V or less, and in many cases, electrical power is supplied from a low-voltage direct-current power supply with a much lower voltage than the high-voltage direct-current power supply. The amplitude of an amplified signal outputted from the drive circuit is on the order of about 10 to 20 V in many cases, and an operating voltage of the drive circuit is generated from the low-voltage direct-current power supply in many cases.
Here, when an event occurs in which an appropriate voltage is not outputted from the low-voltage direct-current power supply or a power supply circuit that generates an operating voltage of the drive circuit from the low-voltage direct-current power supply, the switching element may not be able to be stably controlled. It is not desirable that control of the inverter become unstable when a high voltage is applied to the inverter. Therefore, it is desirable to fix at least the switching element of the inverter in an off state. However, if the operating voltage of the drive circuit is insufficient, then even if the switching element can be placed in an off state, the switching element may go into an on state due to noise, etc. If, in that state, electrical power from the direct-current power supply or induced electromotive force from a device to be driven is supplied to the inverter, then a very large current flows through the switching element and thus it is not desirable.